‘May’s package is built around temporary membership of the customs union, which we are told an overwhelming majority of MPs support.’
Photograph: HO/AFP/Getty Images

Now it’s the lawyers’ turn. Like picadors, they are entering the ring to soften up Theresa May’s deal, before parliament’s serious matadors get to work. They are poking and stabbing and drawing blood. The Commons has ordered the attorney general’s advice to be published in full, against the prime minister’s wishes, and this will be done immediately. At the same time, the European court of justice looks likely to declare that article 50 can be revoked by the UK within the next two years: expert opinion to this effect was submitted to the EJC this week by one of its advocates general, whose findings normally weigh strongly with the court (a ruling is expected soon). Neither is seismic. Both further muddy the waters. But both are a sort of progress.

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The prime minister is foolish. The argument for not publishing the details of what staying in the custom union involves was trivial. Of course “advice is secret”, but it is no time for secrecy when the Brexit debate has been enveloped in mendacity for two years. The attorney general’s bombastic claim on Monday, that concealment was “in the national interest”, was unconvincing.

There is clearly a major legal difficulty about the conduct of the transition period, and the famous backstop as it applies to Ireland. It has never made sense – and no leaver has succeeded in pretending the UK can leave the EU’s customs union without an agreement on the Irish border. As long as Northern Ireland is in the UK it is a cross we have to carry. No agreement, no leave. It is as plain as English. They live in cloud cuckoo land.

Now Brexiters and remainers, hard and soft, can discuss legal realities rather than hysterical rumour. The advice, which is known to be unhelpful to May’s cause, does not seriously damage her already battered cause. It merely restates what we know: that the only available deal remains the only available deal, and it was never going to be wholly palatable.

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That the government was found to be in contempt by 311 votes to 293 is more serious. It indicates major weakness in the loyalty department. It also indicates the poverty of advice available to Downing Street. The vote was surely predictable, and – since the loss is embarrassing – avoidable. Why not concede it in advance? Every Churchill needs his Alanbrooke. May is worryingly short of one.

The effect of a European court of justice decision on article 50 is harder to read. It was sought by a band of remainers, eager to construct circumstances in which a second referendum might include a vote not to leave. But constructing such a referendum gets harder by the day – along with uncertainty as to its outcome. To call one without a new deal on the table would be reckless. It thus must strengthen the case for the deal, if only to move forward.

May’s package has been agreed by the other members of the EU, rather impressively. It is built around temporary membership of the customs union, which we are told an overwhelming majority of MPs support. May has simply got to mobilise them. These representatives must move on to the next stage – and set the economy and the nation’s mind at rest. The deal is only transitional. Both sides will live to fight another day, heaven help us.

• Simon Jenkins is a Guardian columnist

• This article was amended on 5 December 2018 because an earlier version said that the European court of justice had already declared that the UK could unilaterally revoke article 50. Rather, a ruling is pending.